Tensile properties and fracture toughness of chemically-architectured high-entropy alloys

Chemically-architectured materials combine a Ni matrix with a high-entropy alloy (HEA) phase to introduce a controlled chemical gradient. These materials are currently processed through spark plasma sintering (SPS) and are only available in limited quantities. In this work, their tensile properties and fracture toughness were determined for the first time using miniaturized specimens. A tensile yield strength of 476 MPa, a fracture elongation of 23%, and a fracture toughness of 41 MPa ⋅ m were measured for a chemically-architectured alloy exhibiting a steep chemical gradient. For a smoother gradient, the yield stress decreased to 338 MPa while the tensile elongation and fracture toughness increased to 44 % and 125 MPa ⋅ m , respectively. Chemical architecturation resulted in strengthening compared to a reference SPSed HEA, but at the expense of ductility and fracture resistance. Impurity particles located at prior HEA particle boundaries played a critical role in the ductile damage and fracture mechanisms. Earlier void nucleation and accelerated damage development were observed in the material with the steeper chemical gradient, while the softer Ni-rich matrix appeared as a preferred path for fatigue crack propagation. Based on these results, guidelines for further microstructural optimization of these alloys were proposed to improve their mechanical properties.